1. Field of the Invention
The present invention relates to a method of manufacturing a developing roller.
2. Description of Related Art
In conventional electrophotographic printers, the surface of a photosensitive drum is uniformly charged by a charging device. An exposing device emits light which illuminates the charged surface to form an electrostatic latent image on the surface. The electrostatic latent image is subsequently developed into a toner image by a developing device. The toner image is then transferred to a print medium. The print medium is subsequently fed to a fixing device where the toner image on the print medium is fused. The developing device includes a developing roller and a toner tank in which toner is held. The toner is applied to the surface of the photosensitive drum by the developing roller.
Conventional developing rollers use a resilient rubber-like material such as urethane or silicone as a matrix, mixed with a powdered resin such as silicone balls, silica, or glass pieces. These fine powdered resins have diameters in the range of 1 to 50 .mu.m.
The conventional developing roller is manufactured as follows:
A rubber matrix of 100 parts and a powdered resin of 130 parts having a particle diameter in the rage of 1 to 50 .mu.m are mixed together. The mixture is then kneaded. Thereafter, curing agent is added to the kneaded mixture and the mixture is further kneaded. The thus obtained material is then formed into a sheet as a sheeting material.
The sheeting material and an adhesive are applied to a shaft and the shaft is placed in a mold so that the sheeting material is subsequently shaped into a roller. Then the roller is subjected to coarse polishing to remove excessive sheeting material projecting from ends of the shaft. The coarsely polished roller is then subjected to secondary vulcanization, abrasive finishing, and final cleaning successively. After having cleaned finally, the roller is examined before shipping.
During the abrasive finishing, the coarsely polished roller is further polished to a predetermined diameter and a predetermined surface roughness so that the necessary amount of toner is applied to the photosensitive drum.
However, with the aforementioned conventional method of manufacturing a developing roller, particles of powdered resin are ground off the roller together with some of the matrix during the abrasive finishing. As a result, a sufficient number of particles of powdered resin are not left exposed on the surface of the roller. When the surface of the developing roller is ground, the matrix such as rubber plastically stretches to cover the particles of powdered resin as depicted by A-F in FIG. 11, so that the particles will be left partially covered after the roller has been cleaned. Therefore, a sufficient number of particles of powdered resin will not appear on the surface of the roller. Referring to FIG. 11, the particles are exposed as depicted by black areas A-F and covered as depicted by white areas a-f adjacent to the black areas A-F.
As a result, a new, unused developing roller has an insufficient surface roughness, allowing a correspondingly less amount of toner to be deposited on the roller surface. A larger number of particles of powdered resin will appear on the surface of the developing roller reaching a certain number of particles as a larger number of printing operations are performed. Therefore, more amount of toner adheres to the developing roller.
Thus, there will be a difference in print density between a new, unused developing roller and a roller having been used to print, for example, about 5,000 pages of paper.